This invention relates to secondary batteries, and, in particular, to secondary batteries employing zinc electrodes.
Conventional secondary batteries employing zinc electrodes such as, for example, silver-zinc and nickel-zinc alkaline batteries, exhibit a decline in cell capacity with continued cycling. This decline in cell capacity is attributable to the morphological changes, typically referred to as shape changes, which occur in the negative zinc battery electrode. The net effect of these shape changes is aggolomeration and densification of the zinc electrode with a consequent reduction in surface area available for electrochemical reaction.
Various attempts have been made to develop a zinc electrode exhibiting a high resistance to shape change. One technique that has been employed is to incorporate in the active material of the zinc electrode constituents such as calcium or magnesium hydroxide which react with the active material during discharge to form zincates which are substantially insoluble in the cell electrolyte. This technique is disclosed, for example, in U.S. Pat. No. 3,873,367. It has also been proposed to incorporate cadmium particulate matter in the zinc electrode for promoting adherence of electroreduced zinc active material or zinc deposited from the alkaline electrolyte. In this construction the cadmium matter is maintained electrochemically inert during discharge by selecting positive electrode active material to be electrochemically inactive prior to depletion of the zinc active material.
While the above techniques result in a measure of shape change reduction, investigations are still being conducted for alternative techniques.
It is an object of the present invention to provide a zinc electrode which is resistant to shape change.
It is a further object of the present invention to provide such an electrode in a manner which does not reduce battery energy density during use.